Stabilized multivibrator



May 18, 1948. i D. E. KENYON 2,441,579

v I STABILIZED MULTIVIBRATOR I Filed Jan. 6, 1943 29 gal E, I FIG. 3.

. uivEN'roR DAVID E. KENYON ATTORNEY Patented May 18, 1948 STABILIZEDMULTIVIBRATOR David E. Kenyon, Smithtown, N. Y., assignor to The SperryCorporation, a corporation of Delaware Application January 6, 1943,Serial No. 471,518

9 Claims. (01. 250-36) My invention relates to circuits for electricdischarge devices and concerns particularly relaxation oscillators.

It is an object of my invention to provide stabilized oscillators, theoperation andfrequency output of which are substantially unaffected byvariations in supply voltage, load impedance, anode voltage swing, ortube characteristics.

It is also an object of my invention to' provide improved multi-vibratorcircuits.

Other and further. objects and advantages will become apparent as thedescription proceeds.

, In carrying out my invention in its preferred form, I provide a pairof electric discharge devices which may take the form of triode vacuumtubes with conventional capacitance-resistance cross-coupling betweenthe anode of each tube and the control electrode or grid of the other.

tube. However, I provide a variablebias for the control electrode ofeach tube, the magnitude of which is controlled by the circuit of theother tube. In this way, I cause the voltage available for dischargingthe coupling condenser to vary in proportion to the extent'the controlelectrode voltage is driven negative during each oscillation. Bymaintaining a fixed ratio between these two magnitudes, I produceconstancy in the time duration that each tube is maintainednonconducting and thus stabilize the multi-vibrator circuit by producingconstancy of its frequency of oscillation. p

In one form of circuit illustrated inthe drawings, I provide rectifierscoupledto the anode of one tube for supplying the control electrode biasfor the other tube. In another form of my invention, as illustrated, Iprovide cathode resistors in the circuit of one tube for providingcontrol electrode bias for the other tube.

A better understanding of my invention will be afiorded by the followingdetailed description considered in connection with the accompanyingdrawings, and those features which are believed to be novel andpatentable will be pointed out in the claims appendant thereto.

In the drawings, 7

Fig. 1 is a circuit diagram of one embodiment of my invention employingrectifiers for providing bias,

Fig. 2 is a circuit diagram of another embodiment of my invention inwhich cathode resistors are employed for providing variable bias, and

Fig, 3 is a .graphexplanatory of theprinciple of operation of theapparatus.

Like reference characters are used throughout the drawings toindicatelikeparts.

Generally speaking, the frequency of operation of multi-vibrators isdetermined not only swing, since these factors affect the dischargingrate of the grid condensers, the shapeoi the discharge curve and thedepth to which the grid potential is driven. In order to stabilizetheoscillation and make the frequency independent of the factors mentioned,I arrange the control electrode circuits sothat the effects ofvariations in anode voltage swing are compensated. For example, I employvariable bias which varies with anode voltage swing.

In the arrangement illustrated in Fig. 1, variable bias is provided byasymmetrical elements, shown as rectifiers, coupled to, the anodes ofthe discharge devices, as will be explained more in detail hereinafter.The apparatus illustrated in Fig. 1 comprises a pair ofelectricdischarge devices ll and lz, each having anodes l3 and [4, controlelectrodes or grids I5 and I6, and cathodes l'! and I8, respectively.The control electrode I5 is cross-coupled by a coupling condenser 19 tothe anode I4, and similarly, the control electrode I'G is ,cross coupledby a condenser 20 to the anode l3. Grid resistors 2| and 22 areprovided. The grid resistors, however, are not connected to a point orfixed potential but to separate, variable-voltage bias sources. The biasvoltage source for the control electrode [5 comprises a rectifier 23coupled to the anode l4, and the bias source for the control electrode[6 of the discharge device 12 comprises a rectifier 24 coupled to theanode l3 of theopposite discharge device I I. The rectifiers 23 and 24may, if desired, be electric discharge devices of the diode type.

The discharge devices I and [2 maybe triode vacuum tubes as shown anddescribed, and the rectifiers 23 and 24, may be diode vacuum tubes, butit will be understood that my invention is not limited thereto. u

As in conventional multi-vibrator circuits, each of the tubes M and I2is provided with load impedance, represented by the anode resistors 25and 26. A pair of voltage supply terminals 21 and 28 is provided whichmay be connected to the positive and negative sides, respectively, of avoltage source, such as a B battery 29, the negative side of which maybe grounded. In the arrange'mentillustrated in Fig. 1 the oathodes l1and 18 are directly connected to the negative supply terminal 28, andthe resistors 25 and 26 are connectedin series with the anodes l3 andI4, respectively, to the positive supply terminal 21.

In order to supply direct-current or uni-directional bias voltagesproportional to the alternating potentials of the anodes I3 and I4,respectively, coupling condensers 3| and 32 are interposed between theanode l l of'the device I2 and the rectifier"23," and between theanod'eI3and the rectifier 24. For supplying positive bias voltage as shown anddescribed, the rectifiers 23' and 24 are so connected that theircathodes serve as the output terminals to which the grid leak 3! and 32.Filter circuits comprising resistors 33 and 34 and condensers 35 an'd'35, respectively;I-

lo-device to become non-conducting as the first decircuits the dischargedevices become alternately vicebecomes conducting. As the coupling con-1 denser discharges however, the control electrode resistors 2| and 22are connected- The--rect-ifier'--; anodes are connected tothe"couplingcondensersmay also be provided. The time constant of theelements 32 and 34 is preferably large incom peak alternating voltage'or 'thecomplete anode 7 Voltage swing; For example; the =resistors 33and 34 may be replaced by twoadditibrralrectifiers 23A and 24A,respectively; This connection may be accomplishe'win 1 by' providingchange over switches Sfancl- S2" with switch bladesg which whenthrowrrin the upward position respectively connect the -ano'de-- of'the*-reetifie'r 23 -to the cathode" of rectifieiflfiei "and the =anodeof therec'tifier 24 tothe cathode 'of- -therectifier 24A The *rectifiers23A and '24-A have their anodes groundedzj I p Whenthe switches S1 *andSal-"are transferred from theposit-io'n' illustrated to the upward position,'- so"th'a t' the re ctiflrs23Kand"-24A are con-'- neoted, therectifieFcircuitstogether with the coupling condensers '3 I" and 32 actas'voltag-e donblers: The'f recliners-23fi-rand 24ie -preven-tthan'odesof therectifiers 23 and"24 fronr falling below ground' potential.Consequently; 'the con'-' densers 3 Iand 32-" are charged" whenever the'po tentials of 'tlfe"anodes--I3 'and I4fall'; and the chargesaccumulate'd during the negative half cycles ofanodevoltagepass throughthe'rectifiers 23" and 24- to'the condensers "35 and 36 during thepositive'ha'lfcycles'pf' ano dc voltage I at l theanodes I 3 and'- I4:The result is tha-t"-the *condensers 3 5"and36"areprogressively chargedwith higher andliigher'p'otential's'; until the condenser 35 has reached'a potential equallin'g thevoltage swing of the anode I4 andthe'*condenser36 -has reached "9, potential "equalling?the voltage swingof the "anode I 3." 'rne-eondensers 3' I f 32', 35 and 35 arerelatively-large so thatnoappreciable va'riationin' the accumulatedcharge takes place so long'asther'e' is no change in the voltageswing ofthe -devioe-which--has been non-conducting gradually rises toicut-oii,causing the latter device to become conducting and to drive the controlelectrode of the first device negative beyond cu t-off, Thus, eachdischarge device tends to approacha quiescent condition in which it isconducting, but in so doing it extinguishes the current. new'inithefother device; If the control electrodes 'arefbias'ed toground'potential :or' to some other fixed potential the timerequired forthe coupling Jcondenser to discharge sufiiciently to permit lthe-"control:electrod'e to' rise to cut-off is ivariedvlbyw' various?factors: and these factors, thereforerinfiuencetheinon-conducting periodof the dischargesdevi'ce and "-theoscillation irequ'encywfithe circuit;The :charge": collected by the coupling condenser :rdepen'ds'iupon" the-magnitud'e' 'of :thersupply wolta'ge: source 2 9 and the extent owhichahevcontrol electrode'is driven negative dependsrupon the voltageswing of the anode ofthe* other device; whichgi in turn, depends uponthe load impedance' and A the 1 characteristie curve oflthediscl-rarge;device." For a given load resistance the anode voltage".swing depends upon the-sane de cathode "current or discharge rurrento-fithe device:- The'effect'of these factor-s isovercome-in':accordancewith my invention becausethe control electrodes areseparately biased by' connecting them to bias points the potentials"fiwhich vary to? compensate for variations in h anodvoltagefiswing ofthe discharge device whi'ch'corrtrols the control electrode oftheotheraievice:

Assuming thet at the instant of initial considratio hie-discharge device"I I is :conducting andthe discharge device I 2 i's -non-conducting,

by the supply voltage of source 29 sincelthe anode I 4- isat theqootential or the; positivesupply terminal 2 i and the control-'electrodel 5 ii is substantially at zero: on ground: potential. Owing tothe characteristics "of the discharge devices I I and I 2 the controlelectrode potential cannot rise above zero!" The potential of thecathode of the rectifier 23 1s aea value E1 which-is the value -ofthanode voltage swing of the anode IQP -Cfirrent tendstonew: inthe gridleak resistor 21fbut for the -reason ju'ststated, the control electrodeIB rem'ains at Zer or ground potential.

At some -later instanti wh I the- -potential-of" the control electrodeIfi has risen to' cut oft; the discharge device I2 becomes cond""ing,.;-abr uptly, itsanodevonage faiis abr-uptly y new 'of-eurrent inthe load impedanee "2t; and the potential of the control electrode I5 is"driven sharply negative The v 'alue of the negative potentiar ofw-hihthe corrtroi electrode I5 is instantan ously repres'erzdaed1as?E2.In

*3 the"- bias potential provid'ed by the condenser 35 is represented asEi -and th'e negative anode voltage swing throng --Whi'6h'-'th controlelectrode I5 has' be'eri drive Ea?" The voltage chaiige acting -in thetdischarge E1+E2 and the condenser 19 tends to discharge along a curve 21(Fig. 3) whichis asymptotic to the value of E1. The reason for this willbe apparent from a consideration of the nature of the condenserdischarge.

The discharge curve of a condenser representing the change in voltageacross, the plates produced by a disturbance changing the voltagesacting in the discharge circuit of the condenser is determined by thedifference between the voltages in the discharge circuit before andafter the disturbance. In the case of the coupling condenser l9, thischange in voltage is the sum of the bias voltage provided by thecondenser 35, represented by the symbol E1, and the anode voltage swingof the discharge device l2, represented by the symbol E2. In Fig. 3 thepotential ofthe control electrode IS with respect to ground isrepresented by the discharge curve 31, which is drawn with voltagemeasured in the vertical direction and time in the horizontal direction.While the discharge device II is still conducting, the potential of itscontrol electrode is fixed at zero, because electron fiow in the devicel I would prevent its control electrode from becoming positive, and thebias potential E1 provided by the rectifier '23 and the condenser 35 hasno eifect on the condenser l9. Then at the instant the device it?becomes conducting the potential ,of the control electrode is drivennegative through the voltage E2. The control electrode is now free tofloat at the potential determined by the coupling condenser charge. Oneplate of the condenser 19 is now efiectively connected through the gridleak H to the cathode of the rectifier 23 which is at E1 volts; theother plate, connected to the anode M of the device l2, must fall E2volts. The total change in voltage acting in the condenser dischargecircuit is therefore E1+E2, and the discharge curve 3! is asymptotic tothe line E1 in Fig. 3. For convenience, the difierence between zeropotential and the actual cut-oif potential of the control electrode isdisregarded since the negative voltage swing is made very large incomparison with the actual cut-off voltage. V

The time required for the potential of the control electrode to rise tothe value zero, represented in Fig. 3 by the symbol it, determines thetime that the discharge device ll remains non-conductive, If the circuitconditions should be changed by reason of a change in voltage supply, inthe impedance of the load impedance 26, or in the characteristics of thedevice 12, E1 and E2 will change in the same proportion since they havebeen made equal. The discharge curve31 will become more or less steepthan is illustrated in Fig. 3. However, the time durationtwill remainunchanged. Since the curve 31 is exponential, the time required for theordinate to rise to a fixed proportion of the total change is constanteven though the total change in voltage may be varied. Consequently, thenon-conducting period of the discharge device H is stabilized and isindependent of the various factors mentioned which vary with changes incircuit conditions. In a similar manner, the non-conducting period ofthe discharge device I2 is stabilized and the frequency of themultivibrator circuit is stabilized. Within reasonable limits, Ihaveeven found it possible to replace one pair of electric dischargedevices H and [2 of a given type and make by another pair of somewhatdifferent type and make without causing variation in the frequency ofthe multievibrator. circuit.

In the operation as explained, it was assumed that the bias potential E1was equal to the negative swing E2 of the control electrode. However,the same stability would be obtained if some other fixed ratio weremaintained between the value E1 and the value E2, equality of the twovalues not being necessary. For example, if the switches S1 and S2 aremoved to the downward positions, the condensers 35 and 36 will becharged to potentials respectively equalling the peak alternatingvoltages of the anodes I4 and i3 or one-half the anode voltage swings.Nevertheless, a fixed proportion is maintained between the magnitudes ofthe voltages E1 and E2, discussed in connection with Fig. 3, andstability of oscillation is obtained. If desired, the circuit may bemodified to maintain'any other convenient ratio between the biaspotential of each discharge device and the voltage swing of the anode ofthe other discharge device. 7

In the arrangement of Fig. 1, with the switches 81 and S2 in thedownward positions, the potentials of the condensers '35 and 36 maycontinuously equal one-half the respective anode voltage swingsprecisely only if it is assumed that the resistors 33 and 34 are largein relation to the resistors 25 and 26 respectively, and that the gridleak resistors 2| and 22, in turn, are large in relation to theresistors '25 and 26. However, these assumed resistance relationshipsare not necessary to the satisfactory operation of the circuit. Formaximum stability, nevertheless, I prefer to utilize resistancerelationships substantially as assumed.

As pointed out, the control electrodes I5 and 16 are provided withpositive biases which are equal to a substantially constant fraction ofthe anode voltage swings ofthe opposite tubes and which compensate forvariations in swing which may be produced by variations in the voltageof the supply source 29, variations in the load impedances 25 and 26, orvariations in tube characteristics. Each tube stage forms a portion of acontrol circuit for the other so that I may stabilize each stage bycompensating variation in the other.

In place of using separate rectifiers for supplying the bias voltages, Imay modify the circuits of the main tubes l I and [2 so that each willprovide a bias voltage for the control electrode of the other tube. Forexample, as illustrated in Fig. 2, the tubes II and I2 are provided withcathode resistors 39 and 40, respectively, connected between thecathodes H and I8, and the negative supply terminal 28. 2| is connectedbetween the control electrode 15 and the cathode l8 of the other tubel2, and likewise, the grid resistor 22 is connected between the controlelectrode l6 and cathode l'l.

In this case the control electrode of each discharge device is biased tothe potential of the cathode of the opopsite discharge device when thelatter is conducting. Considering the coupling condenser l9, andreferring to Fig. 3, E1 is the voltage across the resistor 40 when thedevice 12 is conducting. As before, E2 is the anode voltage swing of thedevice I2. E1 and E2 are both proportional to the anode-cathode currentor discharge current of the electric discharge device l2. Assumingconstant ratio of the resistances of the elements 26 and 40, the ratioof E1 to E2 remains constant and the oscillator is stable in frequency.Variations in load impedance have some effect, but other changes incircuit conditions do not vary the oscillator frequency.

For improving the wave from the voltages and The grid resistor.

7 currents appearing in the tubes in the circuit of Fig. 2, by-passcondensers 4i and 42 may be connected across the cathode resistors -39and 40, respectively. I have found that stability is obtained with orwithout such by-pass condensers.

As many changes could be made in the above construction and manyapparently widely diiferent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A stabilized multivibrator, comprising a pair of electric dischargedevices each having an anode, a cathode, and a control electrode, firstand second supply terminals for connection to a current source, a pairof load impedances connected between the first supply terminal and therespective anodes, coupling-condensers connected between the anode ofone discharge device and thecontrol electrode of the other, grid leakresistors connected between the control electrode of one dischargedevice and the cathode of the other, and cathode resistors connectedbetween the respective cathodes and the second supply terminal.

2. Apparatus such as set forth in claim 1, having by-pass condensersconnected across each of the cathode resistors.

3. A stabilized-multivibrator, comprising a pair of electric dischargedevices each having an anode, a cathode, and a control electrode; firstand second supply terminals for connection to a current source; a pairof load impedances connected between the first supply terminal and therespective anodes; cross-couplings between the anode of one device andthe control electrode of the other; and a variable-voltage bias-supplysource connected to each of said control electrodes, each bias-supplysource comprising a rectifier coupled to the anode of the oppositedischarge device.

4. A stabilized multivibrator comprising first and second electricdischarge devices each having a cathode, an anode, and a controlelectrode; first and second impedances respectively connecting thecathodesof said devices to a junction point; means including third andfourth impedances for supplying the respective anodes of said deviceswith positive potentials relative to said junction point; fifthand-sixth impedances coupling the control electrode of said first devicerespectively to-the anode and to the cathode of said second device; andseventh and eighth impedances coupling the control electrode ofsaidsecond device respectively to the anode and to the cathode of saidfirst device. I

5. A stabilized multivibrator comprising first and second electricdischarge devices each having a cathode, an anode, and a controlelectrode; first and second impedances respectively connecting thecathodes of said devices to a junction point; means including third andfourth trode; first and second impedances respectively connecting thecathodes of said devices to a junction point; means including third andfourth impedances for supplying the respective anodes of said deviceswith positivepotentials relative to said junction point; fifth-and sixthimpedances connected in series between the anode and cathode of saidfirst device, the junction thereof being coupled to the controlelectrode of said second device; and seventh and eighth impedancesconnected in series between the anode and cathode of said second device,the junction thereof being coupled to the control electrode of saidfirst device.

'7. A stabilized oscillation generator of the multivibrator type forproducing a signal having a given period, comprising a pair of electricdischarge devices each having an anode, a cathode and a controlelectrode; first and second supply terminals for connection to a currentsource; a pair of load impedances connected between the first supplyterminal and the respective anodes; cross-couplings between theanode ofeach device and the control electrode of the other, said cross-couplingshaving time constants short relative to said period; a direct-currentbias-producing means associated with each of said devices for providinga voltage dependent upon the average amplitude of anode voltage andcurrent variations in the device but substantially independent ofcylical variations thereof; and electrically conductive impedance meansconnecting the direct-current bias-providing means associated with eachdevice to the control electrode of theother device.-

8. A stabilized oscillation generator of the multivibrator type \forproducing a signal having a given period, comprising first and secondelectric discharge devices each having a cathode, an anode and a controlelectrode; first and second supply terminals for connection to a currentsource; a pair of load impedances connected between the first supplyterminal and the re-' spective anodes; a cross-coupling between theanode of the first device and the control electrode of the second deviceand a cross-coupling between the anode of the second device and thecontrol electrode of the first device, said crosscouplings having timeconstants short relative to said period; direct-voltage storage meansconnected to the first device-for producing a direct voltage dependenton the average amplitude of current variations insaid first devicebut'substantially independent of cyclical variations thereofelectrically conductive impedance means coupling said storage means tothe control electrodeof said second device; further direct-voltagestorage means connected to the second device for producing a directvoltage dependent on the average amplitude of current variations in saidsecond device but substantially independent of cyclical variationsthereof; and further electrically conductive impedance means couplingsaid further storage means to the control electrode of said firstdevice.

9. A stabilized multivibrator comprising first and second electricdischarge devices each havinga cathode, an" anode, and a controlelectrode; a pair of load imp'edanc'e's' connected respectively betweensaid anodes and the positive terminal of a source of potential; meansfor applyig to each of saidcontrol electrodes a-unid'irectionalpotential having a magnitude dependent upon the average amplitude' oithe current flowing in the circuit or theopposite anode; and separatemeans for applying to each of said control elee- Number trodes apotential dependent upon the voltage 2,157,533

fluctuations at the opposite anode. 2,254,852 DAVID E. KENYON. 2,282,895

5 2,302,690 REFERENCES CITED The following references are of record inthe 2,154,492 Clough Apr. 19, 1939 Name Date Geiger May 9, 1939 MillerSept 2, 1941 Shepard May 12, 1942 Germeshausen Nov. 24, 1942 FOREIGNPATENTS Country Date Great Britain Nov. 8, 1937 OTHER REFERENCESTransactions AIEE, vol. 60, 1941, pp. 371-376, (Copy in Div. 51.)

Certificate of Correction Patent No. 2,441,579. May 18, 1948.

DAVID E. KENYON It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows: Column 5, line 3, for curve 27 read curve 87; column 6, line61, for opopsite read opposite; line 75, for the word from read form of;and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Ofiice Signed and sealed this 27th day of July, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommiaaz'oner of Patents,

